The present invention relates to a hydrogenated block copolymer having a specific structure; and to a polypropylene resin composition which comprises a polypropylene resin and the hydrogenated block copolymer having a specific structure, which composition is improved in the balance among flexibility, stress-whitening property, haze and film blocking property by the incorporation of the hydrogenated block copolymer.
Since polypropylene resin compositions are generally excellent in chemical resistance and mechanical properties, they are used widely for packing materials, sundries, machine parts, automobile parts and the like. In addition, development of halogen-free transparent polymer materials has recently been carried out briskly, forced by the necessity for environmental protection. There is a demand for development of flexible and transparent polypropylene resins particularly in the fields of sheets or films. It is the common practice to add an elastomer to a polypropylene resin in order to make the resin flexible and transparent. By the addition of an olefin type elastomer to a polypropylene resin, flexibility can be improved, however, the stress-whitening property and haze are not satisfactory.
In JP-A-61-155446 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent application), claimed is a composition comprising a hydrogenated block copolymer having a predetermined number-average molecular weight, a predetermined amount of styrene and a predetermined amount of a hydrogenated polybutadiene block at the terminal of the copolymer; and a polyolefin and examples using a styrene-hydrogenated polybutadiene-styrene-hydrogenated polybutadiene block copolymer or a hydrogenated polybutadiene-styrene-hydrogenated polybutadiene-styrene-hydrogenated polybutadiene block copolymer having at the terminal thereof a hydrogenated polybutadiene block in an amount of 1.3, 2.5, 3, 5, 6.7, 10, 20 or 40 wt % are described. In the specification, it is described how the amount of the terminal hydrogenated polybutadiene block influences on the mechanical strength or rubber elasticity of the composition. It does not include an example using a hydrogenated block copolymer having a terminal hydrogenated polybutadiene block wherein the average of 1,2-bond amount, before hydrogenation, of a polymer block mainly comprising a butadiene monomer falls within a range of at least 62 mol % but less than 99 mol %. The publication includes neither a description nor suggestion concerning the structure of the hydrogenated block copolymer and an improvement in the balance among flexibility, stress-whitening property, haze, film blocking property brought by the addition of the hydrogenated block copolymer to a polypropylene resin.
In JP-A-6-287365, a composition comprising polypropylene and a hydrogenated diene copolymer is proposed with a view to improving the stress-whitening property. The film obtained by this process, however, is accompanied with such a problem as a deterioration in blocking property between the obtained films and an improvement is demanded. The film is also unsatisfactory in flexibility and haze.
An object of the present invention is to provide a polypropylene resin composition well-balanced in flexibility, stress-whitening property, haze and film blocking property and also a hydrogenated block copolymer for obtaining the composition.
With a view to attaining the above-described objects, the present inventors have carried out an extensive investigation. As a result, it has been found that a resin composition comprising a hydrogenated block copolymer having a specific structure and a polypropylene resin effectively attains the above-described objects, leading to the completion of the present invention.
The above-described object of the present invention is attained by the following hydrogenated block copolymers and resin composition.
1. A hydrogenated block copolymer which comprises at least two polymer blocks A each mainly comprising an aromatic vinyl hydrocarbon compound monomer unit and at least two hydrogenated polymer blocks B each mainly comprising a butadiene monomer unit, at least 90% of the olefinically unsaturated double bonds in said polymer block mainly comprising a butadiene monomer unit before hydrogenation having been hydrogenated,
wherein at least one of the block at the terminal of the hydrogenated block copolymer is the polymer block B,
wherein the proportion of the terminal polymer blocks B in the hydrogenated block copolymer is at least 0.1 wt % but less than 9.1 wt %,
wherein the proportion of the aromatic vinyl hydrocarbon compound in the hydrogenated block copolymer exceeds 10 wt % but less than 25 wt %, wherein the 1,2-bond content of the polymer blocks mainly comprising a butadiene monomer unit before hydrogenation is, on average, at least 62 mol % but less than 99 mol %, and
wherein the difference xcex94Tc (Tc1xe2x88x92Tc2) between the crystallization initiating temperature (Tc1) of the isotactic homopolypropylene and the crystallization initiating temperature (Tc2) of a mixture thereof with the hydrogenated block copolymer is at least 1.5xc2x0 C.
2. The hydrogenated block copolymer according to the above embodiment 1, wherein the proportion of the aromatic vinyl hydrocarbon compound in the hydrogenated block copolymer is at least 12 wt % but less than 25 wt %.
3. The hydrogenated block copolymer according to the above embodiment 1, wherein xcex94Tc (Tc1xe2x88x92Tc2) is at least 2.0xc2x0 C.
4. The hydrogenated block copolymer according to the above embodiment 1, wherein the proportion of the terminal polymer block B in the hydrogenated block copolymer exceeds 0.5 wt % but less than 5.0 wt %.
5. A resin composition comprising the following components (1) and (2):
(1) 5 to 99 parts by weight of a polypropylene resin, and
(2) 1 to 95 parts by weight of a hydrogenated block copolymer according to any one of the above embodiments 1 to 4.
The present invention also relates to a sheet and film comprising the above-described resin composition.